Nick Davis, a maritime security expert, said he had received a verbal agreement from Somali pirates holding the British couple to release their captives in exchange for around £100,000 last November.

He said he had raised the ransom money from private donors in Canada, Britain and the United Arab Emirates and would have been able to "hook the Chandlers out" at once had the Foreign Office lent its support.

The plan required a British warship to be stationed off the Somalian coast in readiness to take the couple on board once they had been released. But Mr Davis said the Foreign Office refused to respond to his requests to discuss the proposals and advised the Chandlers' family not to speak to him.

However, an FCO spokesperson said: “We have never attempted to block any activity by Mr Davis.”

Mr and Mrs Chandler, from Tunbridge Wells, Kent, were seized from their yacht the Lynn Rival in the Indian Ocean on October 23 last year.

The pirates initially demanded $7 million (£4.2 million) for their safe release and threatened to kill them if their demands were not met.

But Mr Davis, an ex-military consultant who advises shipping companies on security, said the captors quickly climbed down from their initial demands when they realised the Chandlers were not insured against kidnap.

He said: "Intelligence wise, you need to understand that when pirates turn round and demand $7m, that's not what they mean at all. Once they found out that there was no big maritime insurance group that was going to pay out millions, they started to come down.

"Within the first month, after a couple of locals had got involved and they had realised that this was a private couple who had no money and no house, we had an agreement from the captors that we'd drop the cash and they would release the couple."

Mr Davis, chairman of the Merchant Maritime Warfare Centre, said he put together a full rescue package that required a British warship to be stationed off the coast of Somalia.

"When you're dealing with a merchant vessel that's been hijacked, the minute the pirates release the ship the crew can just turn off the engine and drive away. But this was a situation where we had two individuals being held on land, with no transport," he said.

"We put together a very simple plan to drop the money at a predetermined position. I wanted a warship stationed offshore so that the couple could be driven out on a skiff and taken on board to safety. But the Foreign Office didn't want to play that game."

The bulk of the payout is understood to have come from family, friends and well-wishers, some of them in the Somali diaspora who are angered at the negative image piracy brings to their nation.

British Government officials have denied claimsthat they funded the ransom indirectly through aid money to Somalia.

Mr Davis added: "When Paul and Rachel find out that so many people were offering to help them and were in contact with the pirates, but that they were stuck there for a year because the Foreign Office wouldn't help, I expect they will be pretty hacked off."

The Foreign Office refused to comment on Mr Davis's claims. A spokesman said: “We have never attempted to block any activity by Mr Davis.”

A spokesman for relatives of the Chandlers said the family had never been represented by Mr Davis and wished to distance themselves from his claims.

Aden Sylvin, a chief advisor to the Somali government and former member of the French Foreign Legion, said that he had been involved in negotiations since day one of the capture and claimed that the rescue could not have been brought about any faster.

“To be honest with you we did everything we could to rescue those people,” he said.